Variable voltage transformer



Sept. 26, 1933. w s WERNER 1,928,343

VARIABLE VOLTAGE TRANSFORMER Filed Jan. 19, 1933 INVENTOR. M45111? 5. Wmvs/e ziozzf ATTORNEY.

Patented Sept. 26, 1933 VARIABLE VOLTAGE TRANSFORMER Wilbur S. Werner,South Fort Mitchell, (lovington, Ky., assignor to Kelley-Koett Mfg. C0,,Inc., Covington, Ky., a corporation 01' Ohio Application January 19,1933. Serial No. 652,525

7 Claims. (Cl. 171-119) This invention relates to a variable voltagetransformer.

Among the objects of the invention are to produce an apparatus of thiskind, the voltage of the output of which may be changed by extremelysmall degrees and with no abruptness at any stage. It is aimed toproduce a transformer voltage regulator the output, voltage of which maybe varied under load without the breaking of the circuit at any time. Athird object is to produce an apparatus of high power factor, and such aconstruction has been achieved;

Referring to the accompanying drawing, Fig. 1 is a front elevation of mytransformer. 5- Fig. 2 is a side elevation in section, this being takenon line 2-2 of Fig l. Fig. 3 is a sectional plan view, the section beingU taken on line 3-3 of Fig. 1.

' Fig. 4 is a schematic wiring diagram illustratmg the principleinvolved. A

In the. drawing, 10 is a bundle of iron core lamlnations of the shelltype. The middle leg, which is built up to circular section is indicatedby 11. Holding the laminations together in all of the legs are two pairsof angle irons, the upper set of which are marked 12 while 13 indicatesthe lower set. These angled beams, of which there is a front member anda rear member in each set, are distinguished in Figs. 2 and 3 as 13a and131), the latter being the rear member. 12a and 121) are also sodifferentiated on Fig. 2. Bolts 29 hold the angle iron pairs together.

Encircling the middle leg 11 there is a bakelite or fiber drum 14 whichbears the secondary winding 16 which is made of flat bare wire and whichmay be wound to form a helix in a spiral groove previously cut in thedrum. The leads of the primary winding are shown at 17 on Fig. 1 whilethe primary winding itself appears as 18 on Figs. 2 and 3, wound closelyabout the middle leg 11, yet separated by only a short distance from thesecondary. .The edge of the drum 14 rests upon a plurality of lowerrollers 19, the holders of which may be attached to the angle irons 13aand 13b. An upper set of rollers 20 also shown in Figs. 1 and 2, arecarried on the upper angle irons 12 and guide the upper edge of the drum14. Actually these rollers 20 rest upon the side oi. a spur ring gear 21which encircles the drum 14 near the top thereof and is the means fortransmitting power for the rotation of the drum when a change in voltageis to be made. This spur ring gear consists of a plurality of insulatedsegments so that it does not form a short circuited turn on thetransformer.

on its contacting surface to accommodate the flat wire of the winding 16which projects from the drum for a distance which is at least half ofthe wire thickness. The arm 26 is slidably carried by two upright barswhich have smooth surfaces.

The uprights are in turn, carried between angle irons 12a and 13a. Thebrushes 15 are insulated from the cross arm 26, and carry a loose lead27 which may be attached to the utilizing circuit.

Attached to the lower end of the drum 14 at the end of the secondarywinding is a brush holder and pair of brushes, the assembly being ingeneral designated by 28; Each brush in this assembly in electricalcommunication with the other.

Below the secondary, and arranged radially about the path of the drumare a plurality of conducting segments 30. The rollers 19 do not makecontact'with these, but the brushes 28 do. Each segment is connected bymeans of an individual wire 31, to one lead 32 of the secondary output.This lead being of opposite polarity from lead 27. Each wire 31 is ledout of the transformer through one of the outer legs of the core. Eachwire 31 makes its exit from the core between the laminations thereof butat a different point,.that is, between diilerent laminations than itsneighbors. Thesepoints are not selected at random, but are carefullychosen so that the series of points shall give definite and uniformdifferences in the amount of core and consequently 01' magnetic fluxbetween them. In this way, means are provided for varying the indicatedvoltage by the insertion or elimination of flux interlinkage of thesecondary circuit by uniform gradations. The wires 31 are connected tothe segments so that the latter are at a uniform graduated series ofpotentials. I

Since there is, in operation, a difference of potential between theneighboring segments, and under some conditions of use these differencesmay be suiiicient to cause damage if brush 23 shoufld make contact withmore than one segment, I have provided a means for making such shortcircuiting harmiees. The means adopted is choke coil 33, which isadapted to act to limit the current flow. In the choke 34, is alaminated or solid iron core which is preferably of toroidal shape.Wires 31 are wound a few timessay one or two, about one leg of this corebefore being attached to the output lead. In order to reduce theinductance of this coil as a whole, the individual coils are woundopposed. This is done by winding every other coil in the same direction.The choke coil may be replaced by resistances.

Referring to Fig. 4, this diagram is numbered as to its symbols tocorrespond with the numbering of the actual parts in the previousfigures. From this diagram the principles involved will be at once clearto those skilled in the art.

The mechanical operation of my variable voltage transformer and theelectrical effects thereof, are as follows: Current is supplied to leads17. Primary winding '18 is energized directly and secondary winding 16inductively. To vary the voltage taken from the secondary, electricmotor 22 is energized, thus rotating drum 14. In the figures shown,rotating the drum clockwise results in a decrease in potential of thesecondary winding and vice-versa. This is brought about by two actions,namely, the vertical movement of brushes 15 which follow the wire on thesecondary by reason of the screw effect thereof; and the rotary movementof brush 28 over segments 30. The first of these acts to alter thenumber of turns of the secondary, while the second'results in a changeof the flux interlinkages of the secondary in steps of less than a fullturn. By reducing the size of segments 30 and by increasing theirnumber, the size of the voltage steps obtainable can be made exceedinglysmall.

If the moving brush 28 stops so that it rests on two contacts, theresulting short circuit current is held to a small value by reason ofthe presence in the circuit of the choke coil 33; the opposing windingsof this coil act so that supposing that v the value of the inductance,when brush rests on a single segment 30, is L, the value when it-restsupon two contacts, bringing about a short circuit, is 4 L, so thecurrent is limited. If resistances are used, supposing the resistance ofthe circuit when brush 31 is contacting only one segment to be R, theresistance when shorting segments would be A R, but the resistanceagainst a short circuit current would be 2 R.

By proper design of the inductance core so that the main load currentsaturates it, but the short circuit current does not, the pulsation ofseries reactance may be further reduced.

The choke coil or corresponding resistance may be omitted from thetransformer if low voltages are handled.

It will be noted that both the brushes 15 and 28 move simultaneously. Bysuch simultaneous movement twoelectrical adjustments are made at once,or more strictly speaking, one electrical and one magnetic adjustment.By reason of this simultaneous movement it is possible to extend greatlythe range of duty of the regulating means altho not interfering greatlywith its delicacy. In order to arrive at any selected voltage, the drum14 is revolved while the operator watches the voltmeter. Rotation isstopped when the desired value is reached.

I claim:

1. In a transformer having a laminated core, means for smoothly varyingthe number of secondary turns in the circuit, means for varying theamount of flux interlinked with the secondary circuit, said latter meansbeing operable simul-.

taneously with the first named means and including a plurality ofsecondary leads making exit from the transformer between the corelaminations thereof at fixed points constituting a graduated series offiux interlinkage steps.

2. In a transformer, a laminated core, a primary, a secondary, means forvarying the number of turns in the latter circuit while permittingcurrent to pass continuously thru said means and means coactingtherewith for varying the number of laminations of the core magneticallylinked with the secondary circuit while permitting current to passcontinuously thru said means and said secondary circuit said meansincluding a plurality of secondary leads making exit from thetransformer between the core laminations thereof at fixed pointsconstituting a graduated series of flux interlinkage steps.

3. In a transformer, a shell type core, a primary winding on the middleleg thereof, an insulating drum encircling said leg, a primary windingabout the middle leg and a secondary about the said leg and said drum,means for rotating said drum, means actuated by said rotation forvarying the number of secondary turns in the circuit and means alsoactuated by the rotation of the drum for varying the amount of fluxinterlinkage in the transformer circuits said means including a plu-.rality of secondary leads making exit from the transformer between thecore laminations thereof at fixed points constituting a. graduatedseries flux interlinkage steps.

4. In a transformer, a shell type core, a primary winding on the middleleg of said core, an insulating drum encircling the middle leg andprimary winding thereon, a secondary wound upon the said drum, a brushin moving contact with a point on the secondary, a brush at the lowerend of the secondary, means for revolving the drum together with saidlatter brush and a series of contacts along the path of said latterbrush, a conductor joining each contact with one arm of the secondaryoutput circuit, each one of said conductors being joinedthereto thru apart of the core giving a different flux interlinkage to the currentwhen it flows thru said conductor.

5. .A transformer according to claim 4 having,

the conductors which give the variable flux interlinkage, wound into achoke coil before joining an arm of the secondary output circuit.

6. In a transformer, a shell type laminated core, a primary wound aboutthe middle leg of the core, a non-conducting drum encircling said legand said primary, a secondary of rectangular section bare wire wound onsaid drum to form a helix, a brush in continuous contact therewith andvertically movable by the rotation of said drum, one lead of the outputcircuit attached to said brush, means for rotatably supporting the drumand for rotating the drum, a brush attached to the end of the secondaryhelix at the lower end of the drum, segmental contacts below said drum,said lower brush making contact therewith, a conductor attached to eachsegmental contact and being led out of the transformer thru a differentportion of the laminations of the core to produce a series of graduatedsteps of varying flux interlinkage of the core with the secondary andeach such conductor being finally joined to. the other lead of theoutput circuit.

'7. A transformer according to claim 6 in which the last mentioned fluxinterlinkage varying leads are wound into a choke coil before beingjoined to a lead of the output circuit.

WILBUR S. WERNER.

